57 



disk. As it passes the stationary zero mark on the scale a red flash 

 is seen like a blurred pointer of fire about an eighth of an inch wide. 

 Then when the incoming echoes come in there is another similar red 

 flash opposite the proper depth on the indicator, if all is working 

 well. Very often there are confusing stray flashes caused by break- 

 ing waves, outside noises, electric currents, etc. 



It is indeed fascinating, and often comforting to the navigator, 

 to be able to steam along taking 150 soundings a minute and watching 

 the depths var}^ automatically with the red light with such precision, 

 as to delineate to the fathom every lump and hollow, every ridge and 

 trough of the ocean floor. The white Ught or deep-water method is 

 slower because of the time necessary to keep the incoming echoes 

 properly compared with the right outgoing signals, and to allow time 

 for the sounds to go down to the bottom and back at the rate of about 

 5,000 feet per second. When everything was working properly it 

 was possible to take in depths of 1,000 fathoms or more, about as 

 many soundings in every minute as would be possible with a wire 

 and weight in a 12-hour day. 



Notwithstanding their limitations and shortcomings the echo depth 

 fioders were invaluable navigational aids on ice patrol. They were 

 especially useful in keeping track of the vessel's position during foggy 

 and cloudy weather and at night, in telling exact points where certain 

 contour lines were crossed, in locating the position of the ship on a 

 line of position or radio bearing line, and in telling quickly the depth 

 of water where an oceanographic station was about to be taken. 



The soundings that were taken when the geographical positions of 

 the ships were very well and fairly well known were saved in a smooth 

 record book. Each sounding so recorded meant not just one depth 

 but the mean of several carefully taken over, say, a minute of time, 

 depending more or less on the plainness with which the echoes were 

 heard. If they were faint many would be listened for in order to 

 be sure to have the depth just right. 



The accepted soundings were corrected by various amounts ranging 

 up to about 5 per cent to allow for variations in the temperature, 

 salinity, and compression of the water column. The corrections 

 were deduced from the velocity chart published facing page 49 in 

 ice-patrol Bulletin 15, season of 1926. Over 3,000 groups of sound- 

 ings, taken when it was thought that either latitude or longitude 

 could possibly be wrong by as much as 6 nautical miles, were dis- 

 carded. Of course, soundings taken during fog, darkness, and in 

 overcast weather were as accurate as those taken when it was clear; 

 but when the position was in doubt, the values could not be used by 

 hydrographers for amplifying the data on charts. 



Lists containing over 1 ,200 good soundings and positions have been 

 forwarded to the United States Hydrographic Office and to the 



